The Earth overall has warmed at an unprecedented pace in the decades of the 1980s and 1990s and then experienced an warming 'hiatus'. These fast warming and warming 'hiatus' have been spatiotemporally heterogeneous and mixed with even cooling in scattered regions. In this talk, we discuss their major physical causes. Depending upon the assumed importance of the contributions of ocean dynamics and the time-varying aerosol emissions to the observed trends in global-mean surface temperature, we estimate that up to one half of the late twentieth century warming could have been a consequence of natural variability which also explains the warming 'hiatus' in the past 15 years or so. In addition to that, the details of the spatiotemporal evolution of warming over the global land will be discussed.